/Engine/Source/Editor/DetailCustomizations/Public/Customizations/ColorStructCustomization.h
Called when the user clicks in the color block (opens inline color picker)
[FReply](API\Runtime\SlateCore\Input\FReply) OnMouseButtonDownColorBlock ( const [FGeometry](API\Runtime\SlateCore\Layout\FGeometry) & MyGeometry, const [FPointerEvent](API\Runtime\SlateCore\Input\FPointerEvent) & MouseEvent )